The "density" in SSDs is different from the density in filters. In filters, the point is for the substance to get entirely from one side to the other. In SSDs, density refers to how many single-bit "boxes" are available in a certain amount of space. The smaller the manufacturing process, the more "boxes" can fit in the same area. However, the transfer of data happens inside these "boxes," depending on whether they are positively or negatively charged, and so the speed of transfer is not fundamentally related to the "density" of the SSD but more to the structure of the "boxes" and how they are connected.

For the SATA 3Gbps connection you've currently got, a number of SSDs can max it out. The best overall performance in SSDs are ones using the 2nd generation Sandforce controller, but over your connection, you're not going to notice any difference between those and the 2nd place Intel 510 series since the performance differences are not significant unless you're using SATA 6Gbps. And if you can get the Intel 510 series 128GB SSD for $250, I'd jump on it.
Based on some benchmarks I found for your SSD model, the Intel 510 should be roughly twice as fast for most applications, which is as fast as you're going to get without getting a SATA 6Gbps controller. In SATA 6Gbps mode, Brian's review shows that the Intel 510 series SSD gets between 50-100% faster transfer rates in real-world applications compared to the same drive in SATA 3Gbps mode, so the difference is significant.
As far as what controller to get, I haven't done the research on that, so I defer to Brian & his recommendations.

SATA is backward-compatible, so both the Intel 510 & Crucial C300 will run just fine on your 3Gbps SATA connection. They'll just be limited in maximum performance. Between them, the Intel has a performance edge, so I'd go with that.

That may be. It's also interesting that they're planning to make the 720 a PCI express SSD, which allows them to compete in other market segments. The use of SLC in the 720 marks it as enterprise-centric, which differentiates it from other PCIe SSDs currently available. I wonder if Intel has done some research that indicates a movement toward PCIe storage and away from more traditional SATA or SAS connections.

Now I know that Brian & company are under non-disclosure agreements and probably can't comment about this, but the rest of us can.
According to Engadget, Intel plans to ship out a bunch more SSDs this year. The high-capacity 320 series should be out at around the same time as the new enterprise-focused Lyndonville and perhaps a new SLC enterprise SSD may be coming out after that. Also in the July-September timeframe, they're expecting to release an SSD that will work as a cache with hard drives to create a hybrid storage system similar to Seagate's Momentus XT, except compatible with (presumably) any hard drive. And around Christmastime, the roadmap predicts a successor to the 510 series. Perhaps this one will have an Intel controller? We can only wait and see.
The leaked roadmap looks like this:

Regarding reliability in real-world terms, according to the only study I know of that has compared them, most consumer SSDs are not significantly more reliable than hard drives but just fail in different ways. Intel SSDs were the only brand in the study that had significantly better reliability than hard drives.
Obviously, having only one study limits the applicability of the results, but they're useful for comparison and consideration. We shall see in future studies if continually advancing technology makes SSDs more reliable or not.

The 115GB drive is likely to be a little bit slower than the 90GB since it's using fewer NAND blocks. This is a result of using newer higher-capacity 25nm NAND. However, it's a small dip in performance and either of the Sandforce-based Corsair Force SSDs will be much better than the JMicron-based Patriot Warp.
The dip in performance of the 115GB Corsair Force compared to the 90GB Corsair Force is not likely to be noticeable unless you're using both SSDs side by side and you're looking for differences. Since it's going to be your first SSD, I think you made the best choice out of the three: you chose the one with the most capacity and the least price per gigabyte while still retaining very good performance.

I was trying to benchmark the existing hard drive in my netbook and among other things, I thought I'd use IO Meter. So I downloaded and installed it, but when it started up, it didn't look anything like other benchmarking programs. I had to choose the test I wanted to run, so I decided to just choose the "run all" option. After 4 hours, it was still running so I figured I must have done something wrong and stopped it. Then I get a Windows warning that says my free space is dangerously low. This was surprising since my drive was less than half filled, so I looked into it and IO Meter had created a file called iobw.tst that took up 66 GB!! So for anyone else out there who wants to benchmark with IO Meter, whatever you do, don't have it do all the tests or it might fill up your hard drive!
And now that I've shared my little misadventure, can the professional storage reviewers here tell me how I'm supposed to actually use IO Meter please? As you can tell, I'm pretty clueless with this program. :$

With the sustained write speed of most current SSDs, I would imagine it's possible to completely exhaust the write cycles of an SSD in a month or so if it was constantly written to at maximum speed. So it's definitely doable if you have either the money or the sponsors.